The conventional writing pen or white-board pen has to be covered with a pen cap when not in use so as to prevent the ink tube from being exposed to the air to vaporize the ink; otherwise the ink on the pen nib would be dried up to prevent the pen from writing normally. Some users often forget to put the pen cap on a pen after writing; after several days, the pen cap is lost, and the ink tube of the pen is exposed to the air to thus clog the pen.